1. Field of the Invention
The invention relates to methods and systems for “arbitrating” between two sensor output signals in order to select and apply a preferred output for use in a signal processing operation in an electronic throttle system.
2. Background Art
The prior art often teaches use of a plurality of sensors generating respective outputs in response to a common input in order to provide “redundant” signals for use in a subsequent signal processing operation. For example, the prior art teaches use of three sensors measuring the identical property, each generating a respective output in response to the common input, whereupon a controller compares the respective outputs and “rejects” the output that least resembles the others and using one of or averaging the remaining outputs. In this manner, the sensors are said to “vote” for a given representation of the common input, with the majority “winning” the vote.
In order to reduce the costs associated with providing plural redundant sensors, the prior art alternatively deploys sensors in pairs to thereby generate a primary signal and a secondary signal, each similarly responsive to the common input, for use in a subsequent signal processing operation. A controller is programmed to utilize the primary signal as long as it remains “plausible,” with the secondary signal being available for use once the “plausibility” of the primary signal becomes suspect. In its simplest form, the plausibility check of the primary signal may constitute a signal range check, wherein the primary signal is compared to a range of outputs permitted to be associated with an operable primary sensor, with the primary signal being used in the subsequent signal processing operation so long as it remains within the predetermined range. Unfortunately, because the secondary signal is used exclusively when the primary output is deemed “implausible,” a system returning to such exclusive use of the secondary signal becomes susceptible to an operational fault in connection with the secondary sensor.
In a known improvement of the latter approach, an in-range check is also performed on the secondary signal and, if both the primary and secondary signals are “in range,” the plausibility of the primary signal is further tested by comparing the primary output with the secondary signal. In response to the comparison, the primary signal is selected for use in subsequent signal processing so long as the primary and secondary signals are within a prescribed tolerance band with respect to one another. If the primary and secondary signals are not within the prescribed tolerance band of one another, the system adopts a “failure” response characterized by limited system operation. Thus, for example, where this approach is used to select one of the generated outputs from a pair of throttle plate position sensors as a feedback control signal to an engine's electronic throttle control system, the engine goes to a reduced-output “failure” operating condition either when one output is outside of its respective range, or when the difference between “in-range” signals is nonetheless outside of the predetermined tolerance band. Using the failure position means that some throttle availability is lost because the throttle is at a fixed position. Alternatively, the system may resort to using the highest indicating sensor. Using the highest indicating sensor may result in the throttle being run shut and potentially causing an the engine to stall for some failure modes.
It will be appreciated, however, that the dual requirements of “in-range” and “in-tolerance” may force a “failure” operation even when one of the two sensors remains fully operational.